1. Technical Field
The present invention relates to manufacturing of chemical power sources and batteries, and more particularly to mercury-free lead-free button batteries, including alkaline zinc-manganese button batteries and silver oxide button batteries.
2. Description of Related Art
Please refer to FIG. 1 for the typical configuration of a conventional button battery, which comprises a negative cap 10′, a cathode material 20′, a gasket ring 30′, an anode material 40′, a positive can 50′ and a diaphragm 60′ that separates the cathode material 20′ from the anode material 40′. The positive can 50′ and the negative cap 10′ are combined in a buckling manner. The gasket ring 30′ is damped between the positive can 50′ and the negative cap 10′, so as to separate the positive can 50′ from the negative cap 10′. The cathode material 20′ is deposited on an inner bottom of the positive can 50′. The diaphragm 60′ is arranged on the cathode material 20′. The anode material 40′ is arranged between the negative cap 10′ and the diaphragm 60′. The anode material 40′ is mercury-free lead-free zinc gel. Generally, the negative cap 10′ is made by punching an iron sheet or an iron-based metal sheet. Contact between the anode material 40′ and low hydrogen overpotential metals such as iron is likely to lead to hydrogen evolution reaction. Thus, for preventing the anode material 40′ from contacting the metal matrix of the negative cap 10′ and thereby preventing any hydrogen evolution reaction, the existing mercury-free lead-free button battery has the negative cap 10′ plated with a layer of high hydrogen overpotential metal, such as indium or tin, so as to separate the anode material 40′ from the metal matrix of the negative cap 10′, thereby preventing hydrogen evolution reaction otherwise caused by the contact between the anode material 40′ and the metal matrix of the negative cap 10′.
While the foregoing indium- or tin-plated negative cap can, to a certain extent, separate the anode material from the metal matrix of the negative cap, there are still shortcomings existing in the conventional mercury-free lead-free button battery in terms of configuration and function when it is put into practical use. The shortcomings can hinder the mercury-free lead-free button battery from achieving its optimal effectiveness and performance, and are summarized as below.
First, due to its own configuration, the negative cap tends have some electroplating-related problems happening in the indium- or tin-plated layer, such as uneven thickness, less density, porosity, and tendencies towards scratch, removal, oxidization and whiskers. Poor electroplating on the negative cap increases the risk of contact between the anode material and the negative cap's metal matrix made of low hydrogen overpotential metal such as iron. Such contact can lead to hydrogen evolution reaction that generates hydrogen and puts the mercury-free lead-free button battery in risk of expansion, weeping and, even worse, explosion.
Second, in the process of indium- or tin-plating for the negative cap, the negative cap is first overall coated with a layer of indium or tin, and then for better appearance or functionality, the indium or tin coated on the outer surface of the negative cap is chemically removed so that only the indium or tin coated on the inner surface of the negative cap is left. Such a process generates a considerable amount of industrial sewage that contains heavy-metal ions, such as indium, chrome or copper, and is seriously adverse to the environment. In the meanwhile, since indium is a rear and expensive metal, the removed indium causes wasting of resources and heavy burden to the related manufactures.
Third, one more major functional defect of the existing mercury-free lead-free button battery is that when the battery undergoes continuous discharge for heavy loads, there is a risk of expansion or explosion. This is a safety concern that should be addressed
Briefly, the existing devices have serious inherent defects, and there is a need for a novel technical scheme that can solve these problems and make alkaline button batteries get mercury free in a safe and environmentally friendly way.